Multi-mode measurements with a downhole tool using conformable sensors

ABSTRACT

An example downhole tool may include a tool body and a first conformable sensor coupled to the tool body. The first conformation sensor may include a flexible material, a transmitter coupled to the flexible material, and a plurality of receivers coupled to the flexible material. The downhole tool may further include a control unit with a processor and a memory device coupled to the processor, the memory device containing a set of instructions that, when executed by the processor, cause the processor to output control signals to a first combination of the plurality of receivers corresponding to a first operating mode; and output control signals to a second combination of the plurality of receivers corresponding to a second operating mode.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application claims priority to Indian provisionalapplication number 2933/DEL/2013, filed Oct. 3, 2013 and titled“MULTI-MODE MEASUREMENTS WITH A DOWNHOLE TOOL USING CONFORMABLESENSORS,” which is incorporated herein by reference in its entirety forall purposes.

BACKGROUND

The present disclosure relates generally to downhole drilling operationsand, more particularly, to multi-mode measurements with a downhole toolusing conformable sensors. Hydrocarbons, such as oil and gas, arecommonly obtained from subterranean formations that may be locatedonshore or offshore. The development of subterranean operations and theprocesses involved in removing hydrocarbons from a subterraneanformation are complex. Typically, subterranean operations involve anumber of different steps such as, for example, drilling a wellbore at adesired well site, treating the wellbore to optimize production ofhydrocarbons, and performing the necessary steps to produce and processthe hydrocarbons from the subterranean formation. In certain operations,measurements of downhole elements within the wellbore may be generated,including measurements of a casing within the wellbore. Typically, thosemeasurements are limited with respect to their granularity, and smallfeatures within the wellbore may not be identifiable through themeasurements.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the present embodiments and advantagesthereof may be acquired by referring to the following description takenin conjunction with the accompanying drawings, in which like referencenumbers indicate like features.

FIG. 1 is a diagram showing an example downhole tool with conformablesensors, according to aspects of the present disclosure.

FIG. 2 is a diagram showing example antenna windings for a conformablesensor, according to aspects of the present disclosure.

FIG. 3 is a diagram showing an example control system for a downholetool with conformable sensor array, according to aspects of the presentdisclosure.

FIG. 4 is a diagram showing an example antenna operating modes for aconformable sensor, according to aspects of the present disclosure.

FIG. 5 is a block diagram showing an example inversion algorithm formeasurements from a cased environment, according to aspects of thepresent disclosure.

FIG. 6 is a block diagram showing an example inversion algorithm formeasurements from an open hole environment, according to aspects of thepresent disclosure.

FIG. 7 is a diagram showing an illustrative logging while drillingenvironment, according to aspects of the present disclosure.

FIG. 8 is a diagram showing an illustrative wireline loggingenvironment, according to aspects of the present disclosure.

FIG. 9 is a diagram showing an example production environment withmultiple, concentric casings.

While embodiments of this disclosure have been depicted and describedand are defined by reference to exemplary embodiments of the disclosure,such references do not imply a limitation on the disclosure, and no suchlimitation is to be inferred. The subject matter disclosed is capable ofconsiderable modification, alteration, and equivalents in form andfunction, as will occur to those skilled in the pertinent art and havingthe benefit of this disclosure. The depicted and described embodimentsof this disclosure are examples only, and not exhaustive of the scope ofthe disclosure.

DETAILED DESCRIPTION

The present disclosure relates generally to downhole drilling operationsand, more particularly, to multi-mode measurements with a downhole toolusing conformable sensors.

For purposes of this disclosure, an information handling system mayinclude any instrumentality or aggregate of instrumentalities operableto compute, classify, process, transmit, receive, retrieve, originate,switch, store, display, manifest, detect, record, reproduce, handle, orutilize any form of information, intelligence, or data for business,scientific, control, or other purposes. For example, an informationhandling system may be a personal computer, a network storage device, orany other suitable device and may vary in size, shape, performance,functionality, and price. The information handling system may includerandom access memory (RAM), one or more processing resources such as acentral processing unit (CPU) or hardware or software control logic,ROM, and/or other types of nonvolatile memory. Additional components ofthe information handling system may include one or more disk drives, oneor more network ports for communication with external devices as well asvarious input and output (I/O) devices, such as a keyboard, a mouse, anda video display. The information handling system may also include one ormore buses operable to transmit communications between the varioushardware components. It may also include one or more interface unitscapable of transmitting one or more signals to a controller, actuator,or like device.

For the purposes of this disclosure, computer-readable media may includeany instrumentality or aggregation of instrumentalities that may retaindata and/or instructions for a period of time. Computer-readable mediamay include, for example, without limitation, storage media such as adirect access storage device (e.g., a hard disk drive or floppy diskdrive), a sequential access storage device (e.g., a tape disk drive),compact disk, CD-ROM, DVD, RAM, ROM, electrically erasable programmableread-only memory (EEPROM), and/or flash memory; as well ascommunications media such wires, optical fibers, microwaves, radiowaves, and other electromagnetic and/or optical carriers; and/or anycombination of the foregoing.

Illustrative embodiments of the present disclosure are described indetail herein. In the interest of clarity, not all features of an actualimplementation may be described in this specification. It will of coursebe appreciated that in the development of any such actual embodiment,numerous implementation-specific decisions are made to achieve thespecific implementation goals, which will vary from one implementationto another. Moreover, it will be appreciated that such a developmenteffort might be complex and time-consuming, but would nevertheless be aroutine undertaking for those of ordinary skill in the art having thebenefit of the present disclosure.

To facilitate a better understanding of the present disclosure, thefollowing examples of certain embodiments are given. In no way shouldthe following examples be read to limit, or define, the scope of thedisclosure. Embodiments of the present disclosure may be applicable tohorizontal, vertical, deviated, or otherwise nonlinear wellbores in anytype of subterranean formation. Embodiments may be applicable toinjection wells as well as production wells, including hydrocarbonwells. Embodiments may be implemented using a tool that is made suitablefor testing, retrieval and sampling along sections of the formation.Embodiments may be implemented with tools that, for example, may beconveyed through a flow passage in tubular string or using a wireline,slickline, coiled tubing, downhole robot or the like.

The terms “couple,” “coupled,” and “couples” as used herein are intendedto mean either an indirect or a direct connection. Thus, if a firstdevice couples to a second device, that connection may be through adirect connection or through an indirect mechanical or electricalconnection via other devices and connections. Similarly, the term“communicatively coupled” as used herein is intended to mean either adirect or an indirect communication connection. Such connection may be awired or wireless connection such as, for example, Ethernet or LAN. Suchwired and wireless connections are well known to those of ordinary skillin the art and will therefore not be discussed in detail herein. Thus,if a first device communicatively couples to a second device, thatconnection may be through a direct connection, or through an indirectcommunication connection via other devices and connections.

Modern petroleum drilling and production operations demand informationrelating to parameters and conditions downhole. Several methods existfor downhole information collection, including logging-while-drilling(“LWD”) and measurement-while-drilling (“MWD”). In LWD, data istypically collected during the drilling process, thereby avoiding anyneed to remove the drilling assembly to insert a wireline logging tool.LWD consequently allows the driller to make accurate real-timemodifications or corrections to optimize performance while minimizingdown time. MWD is the term for measuring conditions downhole concerningthe movement and location of the drilling assembly while the drillingcontinues. LWD concentrates more on formation parameter measurement.While distinctions between MWD and LWD may exist, the terms MWD and LWDoften are used interchangeably. For the purposes of this disclosure, theterm LWD will be used with the understanding that this term encompassesboth the collection of formation parameters and the collection ofinformation relating to the movement and position of the drillingassembly.

Hydrocarbons may be trapped in porous rock formations thousands of feetbelow the surface. Recovering the hydrocarbons typically requiresdrilling a borehole into the porous rock formation so that thehydrocarbons may be pumped to the surface. Metal pipes, referred to ascasings, may be secured within the borehole as part of the hydrocarbonrecovery operation. FIG. 9 is a diagram showing an example productionenvironment and illustrates casings 1002, 1004, and 1006 disposed withina borehole 1008 in a rock formation 1010. The casings 1002-1004 may beconcentric or nearly concentric and secured within the borehole 1008 andeach other through cement layers 1012, 1014, and 1016. The center casing1002 may comprise a production casing where hydrocarbon from theformation strata 1018 is received at the surface (not shown).

The casings 1002-1006 may serve numerous purposes within a productionand drilling environment, including preventing the borehole 1008 fromcollapsing after it is drilled and/or while it is being drilling,protecting a water table in the formation 1010 from contamination,and/or maintaining pressure within the borehole 1008. Accordingly,damage to the integrity of the casings 1002-1006 may compromise thesepurposes and/or otherwise interfere with drilling operations and/orproduction of the well. Common damage to the casings includes crack andcorrosion, which can be an indication of a defective cement bond betweena casing and the borehole wall. Downhole measurements may be used tosurvey the casings 102-106 to identify damage.

According to aspects of the present disclosure, a downhole tool with atleast one conformable sensor may be placed downhole in either an openhole (non-cased) environment or a cased environment, to measure andsurvey downhole elements, such as downhole casings, boreholes, andformations. As used herein, conformable sensors may comprise planarsensors that are printed or disposed on a flexible material that canconform to the shape of a surface with which it is in contact and mayproduce high resolution, azimuthally sensitive measurements that can beused to visualize that surface. As will be described below, an exampledownhole tool with conformable sensors may comprise one or moreoperating modes which correspond to different speeds, depths, andresolutions of measurements, providing for a fast and accurate imagingof the casing in a cased environment or the borehole/formation in anopen hole environment.

FIG. 1 is a diagram that shows two views of an example downhole tool 100with at least one conformable sensor 112, according to aspects of thepresent disclosure. The downhole tool 100 is shown deployed inconcentric pipes 102 and 104, such as in a cased environment. In certainembodiments, the downhole tool 100 may comprise a wireline survey ormeasurement tool that can be introduced into an open hole (non-cased)environment, a cased environment, or within the bore of a drill stringin a conventional drilling assembly. In certain embodiments, thedownhole tool 100 may be included in a LWD/MWD segment of a bottom holeassembly (BHA) in a conventional drilling assembly. The tool 100 may bephysically and/or communicably coupled to a control unit (not shown) atthe surface through a wireline or slickline, or any other conveyance, orthrough a downhole telemetry systems, such as a mud pulse telemetrysystem. The tool 100 may also comprise a control unit that iscommunicably coupled to the conformable sensor 112 of the tool. As usedherein, a control unit may include an information handling system or anyother device that contains at least one processor communicably coupledto a non-transitory computer readable memory device containing a set ofinstructions that when executed by the processor, cause it to performcertain actions. Example processors include microprocessors,microcontrollers, digital signal processors (DSP), application specificintegrated circuits (ASIC), or any other digital or analog circuitryconfigured to interpret and/or execute program instructions and/orprocess data.

At least one conformable sensor 112 may be coupled to a tool body 118 ofthe downhole tool 100. The conformable sensor 112 may include a primarywinding having extended portions for creating an electromagnetic (EM)field in a target, in this case the pipe 102, and secondary windingswithin the primary winding for measuring the current response of thetarget to the generated EM field. The measured current response may beprocessed to identify physical parameters of the target, as will bedescribed below. The resolution of the measurements taken by theconformable sensor 112 may increase as the “stand-off” distance betweenthe sensor 112 and the target decreases.

In the embodiment shown, the conformable sensor 112 is one of an arrayof conformable sensors 110 coupled to a pad 106 that is coupled to andextendable from the tool body 118 through spring mechanisms or motorizedarms 108 to contact the pipe 102. Other locations and arrangements forthe conformable sensor 112 are possible and will be described below. Thespring mechanisms or motorized arms 108 may similarly establish contactbetween the pad 106 and a borehole wall in an open hole environment. Theelasticity of the pad 106 and tension in the arm 108 may be designed insuch a way that the pad 106 will substantially deform to the shape ofthe pipe 102, decreasing the stand off distance between the sensor 112and which may increase the resolution of the resulting measurements.Other pads similar to pad 106 may be arranged on different sides of thetool 100 to mechanically balance the tool 100 within the pipe 102. Inother embodiments, expandable arms may be used opposite the pad 106 tomechanically balance the tool 100. In certain embodiments, the array 110of conformable sensors may be arranged on the pad 106 to perform sensingat different azimuthal positions with respect to the tool body 118. Inembodiments where multiple pads are used, each pad may include an arrayof conformable sensors to perform sensing at different azimuthalpositions, and the pads may be arranged with respect to the tool body118 such that there is full 360 degree coverage around the tool 100,where one pad covers one set of angles, and/or other stations coverother sets, providing full coverage.

As stated above, the conformable sensor 112 may include at least oneportion that functions as a transmitter and generate electromagnetic(EM) fields in a target, such as the pipe 102, and at least one portionthat functions as a receiver that receives and measures the currentresponses of the target to the generated EM fields. In certainembodiments, the downhole tool 100 may comprise separate transmitters114 or receivers 116 mounted on the tool body 118. These additionaltransmitters 114 or receivers 116 may be inductive-type antennas,realized with coils, solenoids, or rotating and/or moving magnets. Incertain embodiments, EM fields may be generated and the correspondingcurrent responses measured with any combination of the transmitter 114,the receiver 112, and the transmitters and receivers within theconformable sensor 112. Notably, when the transmitter is farther awayfrom the receiver, the depth of investigation may increase but themeasurement resolution may decrease.

In use, the downhole tool 100 may generate high resolution measurementsof the pipe 102 by placing the pad 106 in contact with the pipe 102 orother target and transmitting a time-varying EM signal from atransmitter of the conformable sensor 112. The signal may generate eddycurrents in the pipe 102. The eddy currents may generate secondarycurrents that contain information about the pipe 102, and the secondarycurrents may be measured at some or all of the receivers of theconformable sensor 112. Conversely, the downhole tool 100 may generatelow-resolution measurements of the pipe 104 by transmitting atime-varying electromagnetic signal from transmitter 114 and measuringthe current response of the pipe 104 at one or more receivers of theconformable sensor 112.

FIG. 2 is a diagram showing example antenna windings for a conformablesensor, according to aspects of the present disclosure. The windingsshown may comprise the windings for a single conformable sensor and maybe formed by circuit printing or other deposition methods on a flexiblesurface (not shown). As can be seen, the windings include transmittersT1-T4 and staggered receivers R1-RN. The transmitters T1-T4 may compriseprimary windings, while the staggered receivers R1-RN may comprisesecondary windings. The number and size of the receiver pairs maydetermine the granularity and resolution of the measurements. Staggeringthe receivers may double the azimuthal resolution of the sensor sincemore measurements are made per azimuthal position. Although one exampleof antenna windings for a conformable sensor is shown in FIG. 2, otherconfigurations are possible. For example, the size and relativepositions of the transmitters T1-T4 and receivers R1-RN may be altered,and the functionality of the receivers and transmitters can be switched,e.g., T1 may be a receiver and R3 may be a transmitter.

Ports of the transmitting and receiving windings (shown as circles) maybe electrically connected to transmitter and receiver boards (not shown)that cause the transmitters T1-T4 to generate signals and cause thereceivers R1-RN to measure the current responses caused by the generatedsignals. In certain embodiments, one or more of the transmitters T1-T4may generate a signal in a target, and each of the receivers R1-RN mayseparately measure the response of the target to the signal. In certainembodiments, the combinations of transmitters and receivers used togenerate EM signals and measure current responses may be varieddynamically by a control unit coupled to the transmitters T1-T4 andreceivers R1-RN. The number and size of the receiver pairs may determinethe granularity and resolution of the measurements.

In certain embodiments, the conformable sensors may be controlledthrough a control system associated with the downhole tool. FIG. 3 is adiagram showing an example control system 300 for a downhole tool with aconformable sensor, according to aspects of the present disclosure. Thesystem 300 comprises a control unit 302 that may function as the primarycontroller for the tool and may be communicably coupled to transmitters1-N through transmitter electronics 304, to receivers 1-M throughreceiver electronics 306, and to mechanical, electrical or hydraulicelements 330 coupled to and configured to extend pads to which thetransmitters 1-N and receivers 1-M coupled. Other mechanical,electrical, or hydraulic element of the tool may also be coupled to thecontrol unit 302. At least one of the transmitters 1-N and receivers 1-Mmay comprise elements of a conformable sensor or an array of conformablesensors. The transmitter electronics 304 and receiver electronics 306may comprise circuit boards to which some or all of the transmitters 1-Nand receivers 1-M are coupled.

The control unit 302 may trigger the transmitter electronics 304 togenerate a time-varying EM signal through one or more of thetransmitters 1-N. The time-varying signal may be a sinusoidal signal,its phase and amplitude set at a desired value. As is described above,the EM signals generated through the transmitters 1-N may be coupled toand generate eddy currents in the pipe or borehole that are in immediatecontact with the conformable sensors, and the eddy currents may generatesecondary currents that contain information about the pipe or borehole,including features of the pipe or borehole. The secondary currentsgenerated by one or more of the transmitters 1-N of the conformablesensor array may be measured at the receivers 1-M. In the case of afrequency domain operation, the measurements from the receivers 1-M maybe represented as voltage or current numbers in complex domain with realand imaginary parts, in phasor domain as amplitude and phase, or anyother domain that can be obtained by analytical mapping from any ofthese domains. In the case of a time domain operation, the measurementsfrom the receivers 1-M may be represented as magnitudes as a function oftime which can be positive or negative. Results from time and frequencydomain can be transferred from one to another by using Fourier transformor inverse Fourier transform.

The control unit 302 may receive the measurements from the receivers 1-Nthrough the receiver electronics 306 and may transmit the measurementsto the data acquisition unit 308. For a specific transmitter excitation,measurements from multiple receivers can be generated and received atthe same time. Similarly, multiple transmitters 1-N can be excited atthe same time and they can be time, frequency or jointly multiplexed forlatter demultiplexing operation at the receivers. Upon reception at thedata acquisition unit 308, the measurements may be digitized, stored ina data buffer 310, preprocessed at data processing unit 312, and sent tothe surface 314 through a communication unit 316, which may comprise adownhole telemetry system

In certain embodiments, a downhole tool may have multiple operatingmodes, and the control system 300, and in particular the control unit302 may be responsible for controlling the operating modes of thedownhole tool. The operating modes may correspond to differentcombinations of antennas being triggered, different combinations oftransmitters and receivers being triggered, different excitationfrequencies used by the transmitters, and different combinations ofreceivers used to measure the results. For example, one operating modemay comprise a deep sensing mode where transmitters on the tool body areused with receivers in the conformable sensors on pads to increase thedepth of investigation for the tool. Another operating mode may comprisea high resolution mode where the transmitters and receivers on theconformable sensors are used to generate high resolution images of adownhole element.

The control unit 302 may include an algorithm, characterized by a set ofinstructions stored within a memory device of the control unit andexecutable by a processor of the control unit, regarding the operatingmodes to enter depending on the downhole conditions, and may generatecontrol signals to the transmitter electronics 304 and receiverelectronics 306 based, at least in part, on the instructions. In oneexample control algorithm, the control unit 302 may cause the tool tooperate in a normal operating mode, where medium resolution and depth ofinvestigation measurements are taken using a combination of transmittersand receivers on the tool body and the extendable pad. If a feature ofinterest near the tool is identified, the control center 302 may enterinto a high resolution operating mode to provide a robust, azimuthallysensitive image of the feature. In that case, the control unit 302 mayoutput control signals to the transmitter and receivers of a singleconformable sensor azimuthally aligned with the feature, for example, orto two conformable sensors located near each other on an extendable pad.Likewise, if a feature of interest further away from the tool isidentified, the control center may enter into the deep-sensing operatingmode to more fully characterize the feature of interest, in which thecontrol unit 302 outputs control signals to the transmitters andreceivers on the tool body and extendable pads.

In certain embodiments, a control algorithm at the control unit 302 mayalso comprise selection between one or more antenna operating modescorresponding to the individual configurations of the conformablesensors. These antenna operating modes may be used in addition orinstead or the algorithm described above. In certain embodiments, theantenna operating modes may correspond to control signals used totrigger a particular combination of transmitters and receivers in aconfirmable sensor. In other embodiments, the antenna operating modesmay be utilized after the measurements are taken, through processingtechniques that will be described below.

FIG. 4 is a diagram showing example antenna operating modes for aconformable sensor, according to aspects of the present disclosure. Ascan be seen, the antenna modes may correspond to receiver antennawindings similar to those described with reference to FIG. 2. Antennaoperating mode (a) shows a case where a measurement from each receiverin a conformable sensor may be generated and received independently. Inparticular, receiver R1 may make a measurement V1 and receiver R3 maymake a measurement V3 in response to the excitation signal from onetransmitter. The measurements V1 and V3 may be received and individuallyused to characterize the downhole element. Due to independent nature ofthe measurements, this antenna operating mode may provide the highestnumber of data points resulting in the highest resolution image of thedownhole element, with each measurement corresponding to a pixel of theresulting image.

Antenna operating mode (b) shows configuration where the outputs V1 andV3 from receivers R1 and R3, respectively, are combined into a singlemeasurement V13. V13 may comprise a sum of both measurements V1 and V3.In certain embodiments, the summation may be performed at the controlunit of a control system utilizing a binary arithmetic operation, afterthe measurements V1 and V3 are received at the control center. Incertain embodiments, the summation can be performed by hardware coupledto the receivers, such as receiver electronics, when prompted by acontrol signal from a control unit, and the combined measurement may bereceived at the control unit. Antenna operating mode (b) may be usedwhere a higher signal and higher depth of penetration is required thanin antenna operating mode (a), but it will have a lower resolution byreducing the number of data points in the resulting image.

Antenna operating mode (c) is similar to that in (b), but atwo-dimensional combination of receivers is utilized instead of aone-dimensional combination. In particular, the outputs of receiversR1,-R4 are combined into a single measurement V1234. This combinationcan also be performed in software or hardware of a control system.Antenna operating mode (c) will provide higher signal and higher depthof penetration than antenna operating mode (c), with an even lowerresolution.

Antenna operating mode (d) comprises an operating mode which usesmultiple receivers of different sizes at the same sensing position. Theuse of different sized antenna as the same position may allow for aselection between high-low resolution and low-high depth ofpenetration/signal by selecting one of the receivers R1 and R2 to make ameasurements. However, operating mode (d) requires a different wiringconfiguration than the other modes, and may require that the conformablesensor have a specialized design.

Antenna operating mode (e) comprises a periodic operating mode in whicha periodic field distribution is provided by adjusting the polarity ofat least one signal measurement from the receivers. In this case, aspatial distribution of fields with different periodicity can beobtained, which can be used to probe the target features with differentwavelengths. For example, the upper image in (e) shows a periodicitythat is equal to twice of the separation between the receivers, whilethe lower image shows four times the separation. All of the modesdescribed above can be activated or deactivated in real-time or aspost-processing based on the signal levels, depth of penetration, orresolution that needs to be attained based on the application.

According to aspects of the present disclosure, once the measurementsare received, they may be aggregated and processed to produce avisualization of the downhole element being measured or surveyed. Incertain embodiments, aggregating and processing the measurements maycomprise aggregating and processing the measurements using a controlunit located either within the downhole tool or the surface above thedownhole tool. When processed at the surface, the measurements may becommunicated to the surface in real time, such as through a wireline, orstored in a downhole tool and later processed when the tool is retrievedto the surface. In certain embodiments, aggregating and processing themeasurements may comprise aggregating and processing the measurementsusing an inversion algorithm implemented as a set of instructions in thecontrol unit that are executable by a processor of the control unit toperform data calculations and manipulations necessary for the inversionalgorithm. The inversion algorithm may be specific to the environment inwhich the downhole tool is used (cased or open hole) and may be designedto identify different features unique to the environment. Notably,measurements taken using the different operating modes of the downholetool and conformable sensors at similar locations may be combined into asingle, robust image.

FIG. 5 is a block diagram on an example inversion algorithm for a casedenvironment with one or more casings, according to aspects of thepresent disclosure. An input signal 501 may comprise the measurementsfrom the receivers of the downhole tool, including the receivers of theconformable sensor, taken in numerous operating modes. In certainembodiments, the input signals may be divided into windows, such as timefrequency, or space windows. In one example, the measurements from theoperating modes may be divided into azimuthal windows, which are thensubdivided by time and frequency. The measurements for correspondingwindows may be “stacked” or processed together, to improve the signal tonoise ratio and quality of the measurements and the resulting image.

The inversion algorithm may comprise a pre-processing block 502, whichmay receive the input signals. The pre-processing block 502 may processthe input signal 501 to compensate for downhole conditions or to convertthe input signals to a form usable within the inversion block 503. Forexample, the pre-processing block 502 may process the measurements tocalibrate for temperature effects, convert between frequency to timedomain, convert between complex-value to phase and amplitudes, and/or toremove noise by filtering in azimuth or depth.

The inversion algorithm further may comprise an inversion block 503,which may receive and process the signals from the pre-processing block502 to identify parameters of the casings. In certain embodiments, theinversion block 503 may receive a model 504 of the casing or casings inwhich the downhole tool was disposed. The inversion block 503 mayimplement a cost function to identify parameters of the casing orcasings that produce the minimum mismatch between the model 504 and theinput signals 501. The cost function may be defined, for example, byutilizing least squares minimization through L₂ norm. The inversionblock 503 may output data on one or more parameters of the casings.

In certain embodiments, a library 505 of casing responses from othercasings and conformable sensors can be used instead of or in addition tothe model 504. For example, the library 505 may be used if the parameterdimensions of the casing responses are low in number and also small inrange, so that an accurate library can be calculated. If library 505 isused, a multi-dimensional interpolation can be used to obtain theparameters of the casing closest to the measurements.

The inversion block 503 may generate output including one of moreparameters of the casings measured by the downhole tool that may be usedto visualize the casing. Example parameters include the stand-offdistance between the sensors and the casing as well as the thickness,conductivity, permeability, and permittivity of the casing. Because ofthe resolution offered by conformable sensors, very small features (onthe order of 0.1 inches) can be imaged on the casing in direct contactwith the conformable sensor. In the case where tool body transmittersand receivers are used, information on multiple casings may be recovered(pipe index shown as i in the figure). In certain embodiments, thedownhole tool may make measurements as it is lowered to different depthswithin the casing, collecting more data points. These points can becombined to form a log of the casing, providing an image of theparameters of the entire casing, rather than one axial portion.Alternatively, discrete azimuthal measurements from each depth can becombined to obtain an image of the casing. In addition to the pipeparameters, certain environmental parameters, such as temperature, pipestresses, eccentricity of the tool in the borehole or pipe can beobtained.

FIG. 6 is a block diagram on an example inversion algorithm for an openhole environment, according to aspects of the present disclosure. As canbe seen, the inversion algorithm 600 comprises similar features toinversion algorithm 500. For example, the input signals 601 andpre-processing block 602 may be similar to those described with respectto FIG. 4. The inversion block 603 may also be similar, processing theinput signals 601 using a model 604 or library 605, with the a model 604or library 605 corresponding to a borehole rather than a casing.

The inversion block 602 may output parameters specific to an open holeenvironment. For example, the parameters may include a stand-offdistance between the conformable sensor and the borehole, mudconductivity and permittivity, and formation conductivity andpermittivity. Shallow measurements taken using conformable sensors in ahigh resolution mode of a downhole tool may be used to estimate theelectrical properties of drilling fluid within the borehole, and alsoflushed zone and mud cake in the formation. Like the inversion algorithm500, the inversion algorithm 600 may output logs or images that can beused to visualize the entire borehole.

FIG. 7 is a diagram showing a subterranean drilling system 80incorporating a downhole tool 26 with at least one conformable sensorand multiple operating modes, similar to the example downhole toolsdescribed above. The drilling system 80 comprises a drilling platform 2positioned at the surface 82. In the embodiment shown, the surface 82comprises the top of a formation 84 containing one or more rock strataor layers 18 a-c, and the drilling platform 2 may be in contact with thesurface 82. In other embodiments, such as in an off-shore drillingoperation, the surface 82 may be separated from the drilling platform 2by a volume of water.

The drilling system 80 comprises a derrick 4 supported by the drillingplatform 2 and having a traveling block 6 for raising and lowering adrill string 8. A kelly 10 may support the drill string 8 as it islowered through a rotary table 12. A drill bit 14 may be coupled to thedrill string 8 and driven by a downhole motor and/or rotation of thedrill string 8 by the rotary table 12. As bit 14 rotates, it creates aborehole 16 that passes through one or more rock strata or layers 18. Apump 20 may circulate drilling fluid through a feed pipe 22 to kelly 10,downhole through the interior of drill string 8, through orifices indrill bit 14, back to the surface via the annulus around drill string 8,and into a retention pit 24. The drilling fluid transports cuttings fromthe borehole 16 into the pit 24 and aids in maintaining integrity or theborehole 16.

The drilling system 80 may comprise a bottom hole assembly (BHA) coupledto the drill string 8 near the drill bit 14. The BHA may comprisevarious downhole measurement tools and sensors and LWD and MWD elements,including the downhole tool 26 with at least one conformable sensor andmultiple operating modes. As the bit extends the borehole 16 through theformations 18, the tool 26 may collect measurements relating to borehole16 and the formation 84. In certain embodiments, the orientation andposition of the tool 26 may be tracked using, for example, an azimuthalorientation indicator, which may include magnetometers, inclinometers,and/or accelerometers, though other sensor types such as gyroscopes maybe used in some embodiments.

The tools and sensors of the BHA including the tool 26 may becommunicably coupled to a telemetry element 28. The telemetry element 28may transfer measurements from tool 26 to a surface receiver 30 and/orto receive commands from the surface receiver 30. The telemetry element28 may comprise a mud pulse telemetry system, and acoustic telemetrysystem, a wired communications system, a wireless communications system,or any other type of communications system that would be appreciated byone of ordinary skill in the art in view of this disclosure. In certainembodiments, some or all of the measurements taken at the tool 26 mayalso be stored within the tool 26 or the telemetry element 28 for laterretrieval at the surface 82.

In certain embodiments, the drilling system 80 may comprise a surfacecontrol unit 32 positioned at the surface 102. The surface control unit32 may be communicably coupled to the surface receiver 30 and mayreceive measurements from the tool 26 and/or transmit commands to thetool 26 though the surface receiver 30. The surface control unit 32 mayalso receive measurements from the tool 26 when the tool 26 is retrievedat the surface 102. As is described above, the surface control unit 32may process some or all of the measurements from the tool 26 todetermine certain parameters of downhole elements, including theborehole 16 and formation 84, and may also generate visualizations ofthe borehole 16 and formation 84 based, at least in part, on thedetermined parameters through which features of the downhole elements,such as cracks and fractures, may be identified.

At various times during the drilling process, the drill string 8 may beremoved from the borehole 16 as shown in FIG. 8. Once the drill string 8has been removed, measurement/logging operations can be conducted usinga wireline tool 34, e.g., an instrument that is suspended into theborehole 16 by a cable 15 having conductors for transporting power tothe tool and telemetry from the tool body to the surface 102. Thewireline tool 34 may comprise a downhole tool 36 with at least oneconformable sensor and multiple operating modes, similar to the tool 26described above. The tool 36 may be communicatively coupled to the cable15. A logging facility 44 (shown in FIG. 8 as a truck, although it maybe any other structure) may collect measurements from the tool 36, andmay include computing facilities (including, e.g., a controlunit/information handling system) for controlling, processing, storing,and/or visualizing the measurements gathered by the tool 36. Thecomputing facilities may be communicatively coupled to the tool 36 byway of the cable 15. In certain embodiments, the control unit 32 mayserve as the computing facilities of the logging facility 44.

According to aspects of the present disclosure, an example downhole toolmay include a tool body and a first conformable sensor coupled to thetool body. The first conformation sensor may include a flexiblematerial, a transmitter coupled to the flexible material, and aplurality of receivers coupled to the flexible material. The downholetool may further include a control unit with a processor and a memorydevice coupled to the processor, the memory device containing a set ofinstructions that, when executed by the processor, cause the processorto output control signals to a first combination of the plurality ofreceivers corresponding to a first operating mode; and output controlsignals to a second combination of the plurality of receiverscorresponding to a second operating mode.

In certain embodiments, the first conformable sensor is coupled to a padextendable from the tool body. In certain embodiments, the firstoperating mode corresponds to at least one of a first resolution and afirst depth of investigation; and measurements from each of theplurality of receivers. In certain embodiments, the second operatingmode corresponds to a second resolution lower that is than the firstresolution and a second depth of investigation that is higher than thefirst depth of investigation. In certain embodiments, the secondoperating mode corresponds to at least one combined measurement from tworeceivers of the plurality of receivers. In certain embodiments, thesecond operating mode corresponds to a measurement from at least one ofthe plurality of receivers with an altered polarity.

In certain embodiments, the downhole tool further comprises an othertransmitter coupled to the tool body. The set of instructions mayfurther cause the processor to output a control signal to at least theother transmitter and at least one of the plurality receivers of thefirst conformable sensor. In certain embodiments, the set ofinstructions further cause the processor to receive measurements fromthe at least one of the plurality of receivers; and output a controlsignal to the transmitter of the first conformable sensor in response tothe received measurement. In any of the embodiments in this or thepreceding two paragraphs, at least two of the plurality of receiverscomprise different sizes.

According to aspects of the present disclosure, an example method formaking downhole measurement comprises positioning a tool within aborehole, the tool comprising a first conformable sensor that includes aflexible material, a transmitter coupled to the flexible material, and aplurality of receivers coupled to the flexible material. A firstelectromagnetic (EM) signal may be generated using the transmitter. Afirst response of a downhole element to the first EM signal may bemeasured using a first combination of the plurality of receiverscorresponding to a first operating mode. A second EM signal may begenerated using the transmitter. A second response of the downholeelement to the second EM signal may be measured using a secondcombination of the plurality of receivers corresponding to a secondoperating mode.

In certain embodiments, the first operating mode corresponds to a firstresolution and a first depth of investigation. In certain embodiments,the second operating mode corresponds to a second resolution lower thanthe first resolution and a second depth of investigation that is higherthan the first depth of investigation. In certain embodiments, measuringthe first response of the downhole element comprises receiving ameasurement from each of the plurality of receivers. In certainembodiments, measuring the second response of the downhole elementcomprises receiving at least one combined measurement from two receiversof the plurality of receivers. In certain embodiments, measuring thesecond response of the downhole element comprises receiving ameasurement from at least one of the plurality of receivers with analtered polarity.

In certain embodiments, the method may further comprise generating athird EM signal from an other transmitter coupled to the tool, andreceiving a third response of the downhole element to the third EMsignal using at least one of the plurality receivers of the firstconformable sensor. In certain embodiments, the method may furthercomprise receiving a measurement from the at least one of the pluralityof receivers, and outputting a control signal to the transmitter of thefirst conformable sensor in response to the received measurement. In anyof the embodiments described in this paragraph or the preceding twoparagraphs, the first conformable sensor may comprise one of a pluralityof conformable sensors coupled to the tool. In any of the embodimentsdescribed in this paragraph or the preceding two paragraphs, at leasttwo of the plurality of receivers may comprise different sizes.

Therefore, the present invention is well adapted to attain the ends andadvantages mentioned as well as those that are inherent therein. Theparticular embodiments disclosed above are illustrative only, as thepresent invention may be modified and practiced in different butequivalent manners apparent to those skilled in the art having thebenefit of the teachings herein. Furthermore, no limitations areintended to the details of construction or design herein shown, otherthan as described in the claims below. It is therefore evident that theparticular illustrative embodiments disclosed above may be altered ormodified and all such variations are considered within the scope andspirit of the present invention. Also, the terms in the claims havetheir plain, ordinary meaning unless otherwise explicitly and clearlydefined by the patentee. The indefinite articles “a” or “an,” as used inthe claims, are each defined herein to mean one or more than one of theelement that it introduces.

What is claimed is:
 1. A downhole tool, comprising: a tool body; and afirst conformable sensor coupled to the tool body, the first conformablesensor comprising a flexible material; a transmitter coupled to theflexible material; and a plurality of receivers coupled to the flexiblematerial; and a control unit comprising a processor and a memory devicecoupled to the processor, the memory device containing a set ofinstructions that, when executed by the processor, cause the processorto output control signals to a first combination of the plurality ofreceivers corresponding to a first operating mode; and output controlsignals to a second combination of the plurality of receiverscorresponding to a second operating mode.
 2. The downhole tool of claim1, wherein the first conformable sensor is coupled to a pad extendablefrom the tool body.
 3. The downhole tool of claim 1, wherein the firstoperating mode corresponds to at least one of a first resolution and afirst depth of investigation; and measurements from each of theplurality of receivers.
 4. The downhole tool of claim 3, wherein thesecond operating mode corresponds to a second resolution lower that isthan the first resolution and a second depth of investigation that ishigher than the first depth of investigation.
 5. The downhole tool ofclaim 3, wherein the second operating mode corresponds to at least onecombined measurement from two receivers of the plurality of receivers.6. The downhole tool of claim 5, wherein the second operating modecorresponds to a measurement from at least one of the plurality ofreceivers with an altered polarity.
 7. The downhole tool of claim 1,further comprising an other transmitter coupled to the tool body.
 8. Thedownhole tool of claim 7, wherein the set of instructions further causethe processor to output a control signal to at least the othertransmitter and at least one of the plurality receivers of the firstconformable sensor.
 9. The downhole tool of claim 8, wherein the set ofinstructions further cause the processor to receive measurements fromthe at least one of the plurality of receivers; and output a controlsignal to the transmitter of the first conformable sensor in response tothe received measurement.
 10. The downhole tool of any one of claims1-9, wherein at least two of the plurality of receivers comprisedifferent sizes.
 11. A method for making downhole measurement,comprising: positioning a tool within a borehole, the tool comprising afirst conformable sensor that includes a flexible material; atransmitter coupled to the flexible material; and a plurality ofreceivers coupled to the flexible material; generating a firstelectromagnetic (EM) signal using the transmitter; and measuring a firstresponse of a downhole element to the first EM signal using a firstcombination of the plurality of receivers corresponding to a firstoperating mode; generating a second EM signal using the transmitter; andmeasuring a second response of the downhole element to the second EMsignal using a second combination of the plurality of receiverscorresponding to a second operating mode.
 12. The method of claim 11,wherein the first operating mode corresponds to a first resolution and afirst depth of investigation.
 13. The method of claim 12, wherein thesecond operating mode corresponds to a second resolution lower than thefirst resolution and a second depth of investigation that is higher thanthe first depth of investigation.
 14. The method of claim 11, whereinmeasuring the first response of the downhole element comprises receivinga measurement from each of the plurality of receivers.
 15. The method ofclaim 14, wherein measuring the second response of the downhole elementcomprises receiving at least one combined measurement from two receiversof the plurality of receivers.
 16. The method of claim 12, whereinmeasuring the second response of the downhole element comprisesreceiving a measurement from at least one of the plurality of receiverswith an altered polarity.
 17. The method of claim 11, further comprisinggenerating a third EM signal from an other transmitter coupled to thetool; and receiving a third response of the downhole element to thethird EM signal using at least one of the plurality receivers of thefirst conformable sensor.
 18. The method of claim 17, further comprisingreceiving a measurement from the at least one of the plurality ofreceivers; and outputting a control signal to the transmitter of thefirst conformable sensor in response to the received measurement. 19.The method of any one of claim 11, wherein the first conformable sensorcomprise one of a plurality of conformable sensors coupled to the tool.20. The method of any one of claim 11, wherein at least two of theplurality of receivers comprise different sizes.